1. Field of the Invention
This invention relates to image input devices in which the image of a document, such as, for example, a photographic film, is read by means of light that is transmitted through or reflected by the document.
2. Description of Related Art
An image input device includes many components, including: an optical illumination system comprised of an illumination source that is located above a moving source document; a scanner that includes a carriage, which maintains the source document in a (preferably) flat position while moving the source document past the illumination source; and a photographic optical system that focuses light transmitted through or reflected by the source document onto a reading device, such as, for example, a charge-coupled-device (CCD). Light from the illumination source is transmitted and optically focused in a line on the source document, and then light from the source document is focused on the CCD. This light (which is transmitted through or reflected by the source document) is then read as a single line of data. Following the single line of data reading, the scanner moves the source document by a single line increment, changing the position of the original document. The source document is then re-read, scanning of the entire document being accomplished through a repetitive reading and movement process.
An image input device having the structure described above is shown in Japanese Laid-Open Patent Application No. 3-145881, which receives a transparent film or slide as the original source document. A carriage transports the film from a film insertion opening inwardly, and is capable of moving in a reciprocal motion. An optical reading system emits a line of light for imaging the film. At least one part of the path of the light line has an axis that crosses (i.e., is perpendicular to) the direction of transport of the carriage so that the line of light passes through the transparent film source document.
However, as disclosed in Japanese Laid-Open Patent Application No. 3-145881, the carriage which supports and transports the film is mounted to move along a single set of fixed shafts. Accordingly, focus adjustment in the direction of the optical axis of the light that is transmitted through the film is not possible. Because of this, it is preferable that the film be absolutely flat. Symmetry in the image reading operation is not possible if the film is curled. In addition, since the construction provides for the securement of the film to the carriage by means of a plate spring on the carriage into which the film is inserted, depending upon variations in the thickness of the film mount, the surface of the film may completely move, with the problem that the correct focus position cannot be maintained.
In order to provide for an autofocus adjustment operation, a mechanism must be provided to enable the detection of an origin point position relative to the direction of the optical axis of the carriage. As shown in FIG. 2 of Japanese Laid-Open Patent Application No. 3-145881, an optically transparent window (36) is provided in the carriage. When the optically transparent window moves past the light source, an edge of the optically transparent window intersects the light transmitted from the illumination source, which causes the output of an image sensor (e.g., a CCD) to change from high to low. The reading start time of the scanner (i.e., knowledge about the leading edge of the film source document) can then be established on the basis of this signal change.
This arrangement has a drawback in that it causes an increase in the size of the carriage because the transparent window is located in front of the film in the carriage. Additionally, when long strips of film (e.g., having a plurality of frames) are to be read by the image reading device, the carriage must be made very long.
Furthermore, with an image input device in which focus adjustment is possible, in order to detect the origin point position in the axial direction of the light transmitted through the document, heretofore there has been the necessity of detecting the carriage position by means of optical sensors or switches. However, these components are high in cost, and have required a space adequate for their securement.